higher secondary - first year - botany - Textbooks Online

Beneficial Activities of Bacteria
1. Sewage disposal : Organic matter of the sewage is decomposed by
saprotrophic bacteria.
2. Decomposition of plant and animal remains: Saprotrophic bacteria
cause decay and decomposition of dead bodies of plants and animals. They
release gases and salts to atmosphere and soil. Hence these bacteria are
known as nature’s scavengers.
3. Soil fertility :
1. The ammonifying bacteria like Bacillus ramosus and B. mycoides convert
complex proteins in the dead bodies of plants and animals into ammonia
which is later converted into ammonium salts.
2. The nitrifying bacteria such as Nitrobacter, Nitrosomonas convert
ammonium salts into nitrites and nitrates.
3. Nitrogen fixing bacteria such as Azotobacter and Clostridium and
Rhizobium (a symbiotic bacterium) are capable of converting atmospheric
nitrogen into organic nitrogen. All these activities of bacteria increase soil
fertility.
Recycling of matter
Bacteria play a major role in cycling of elements like carbon, oxygen, Nitrogen
and sulphur. Thus they help in maintaining environmental balance. As biological
scavengers they oxidize the organic compounds and set free the locked up carbon
as CO 2
. The nitrogenous organic compounds are decomposed to form ammonia
which is oxidized to nitrite and nitrate ions by the action of nitrifying bacteria.
These ions are used by higher plants to synthesize nitrogenous organic compounds.
The nitrogenous compounds are also oxidized to nitrogen by denitrifying bacteria.
Role of Bacteria in Industry
1. Dairy Industry
Lactic acid bacteria e.g.(Streptococcus lactis) are employed to convert milk
sugar lactose into lactic acid.
C 12
H 22
O 11
+H 2
O 4C 3
H 6
O 3
+Energy
Lactose
Lactic Acid
Different strains of lactic acid bacteria are used to convert milk into curd,
yoghurt(Lactobacillus bulgaricus) and cheese(Lactobacillus
acidophobus).
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